The invention relates to control systems for controlling the activation and deactivation of functional units of a printing machine, for example the throw-on and throw-off of printing cylinders, inking cylinders and other functional units.
Typically, the functional unit to be activated or deactivated is moved by a positioning unit to which the activating or deactivating signal per se is applied. However, such positioning units, such as electrohydraulic or electromagnetic or electromechanical positioning units, usually exhibit dead times in their response to activating (i.e., activating or deactivating) signals. The dead time is in part attributable to the finite time required for energization or deenergization of the electrohydraulic, electromagnetic or electromechanical positioning unit, and is in part attributable to the finite distance through which the positioning unit must move a component of the functional unit (for example a printing cylinder from thrown-off to thrown-on position).
German Democratic Republic patent DL No. 93 784 and U.S. Pat. No. 3,818,827 disclose printing machine control systems operating on a clocked basis. For example, a sheet-representing signal is advanced through successive shift-register stages of a control shift register, under the control of clock pulses applied to the shift register by a synchronizer driven by a rotary reference component of the printing machine. The advancement of the sheet-representing signal through the successive shift-register stages simulates the travel of a sheet through the printing machine. When the sheet-representing signal reaches predetermined successive shift-register stages, functional units of the machine are activated or deactivated, e.g., printing cylinders are thrown on or off. The advancement of the sheet-representing signal from one shift-register stage to the next corresponds to predetermined increments of angular movement of the rotary reference component of the machine.
Proper synchronization can be lost if the machine is operable at a variable speed, and if the dead times of the positioning units (referred to above) are not negligible. The dead time of each positioning unit, when expressed in terms of the extent of angular movement of the rotary reference component of the printing machine, is a function of the angular velocity of the rotary reference component, i.e., of the speed of operation of the printing machine. Accordingly, synchronization based upon the angular position of the rotary reference component cannot be maintained if the speed of operation of the printing machine varies.